Glycogen is the storage form of glucose in animal and human tissues. Moreover it is the polysaccharide molecule that functions as the secondary long-term energy store in animal cell tissue and may be represented as (C6H10O5)n. Glycogen is made up of glucose building blocks, glucose (C6H12O6) being a monosaccharide, or simple sugar and an important carbohydrate in biology. Glycogen is made primarily by the liver and the muscles, but it can also be made by glycogenesis within the brain and stomach. Glycogen is analogous to starch in plants, and is commonly referred to as animal starch, having a similar structure to amylopectin.
Glycogen plays an important role in the glucose cycle as it forms an energy reserve that can be metabolized quickly to meet a sudden need for glucose. Generally, it is the glycogen stored in the liver that is made accessible to other organs and muscles. Muscles themselves utilize their own stores before drawing from the liver. Within the muscle, glycogen is generally found in low concentrations, about 1˜2% of the muscle mass. However, the amount of glycogen stored in a person's body largely is dependent on physical training, metabolic rate and eating habits.
When a meal containing carbohydrates is eaten and digested, blood glucose levels rise and the pancreas releases insulin. Blood glucose enters the liver cells and the insulin acts upon the liver cells to stimulate the action of enzymes including glycogen synthase. Glucose molecules are added together in chains of glycogen so long as the levels of both insulin and glucose remain plentiful. When needed for energy, the glycogen chains are deconstructed and converted back to glucose.
With respect to muscle tissues, glycogen stores within the muscle function as an immediate reserve of energy for the muscle, however muscle cells lack the specific enzyme glucose-6-phosphatase that is required to pass glucose into the blood. As such the glycogen stores within a muscle are for the use of that particular muscle and not shared.
Long distance and endurance athletes such as cyclists, marathon runners and triathletes frequently experience glycogen debt wherein nearly all of the athlete's glycogen stores are depleted after long periods of exertion without sufficient energy replacement through intake of foods and supplements. A phenomena commonly referred to as “hitting the wall” it is an experience most amateur and pro athletes seek to avoid for its onset usually signals the end of good performance, if not the simple ability to continue participation in the activity.
Developing glycogen stores in the muscles themselves is highly desirable for many amateur and pro athletes, for the muscle glycogen stores are immediately available and do not have to be delivered by the circulation of blood from the liver. Significant training and dietary structure can and often is dedicated towards the development and conditioning of muscles to produce and store high quantities of glycogen.
How much glycogen is present at the start of an event can therefore be a significant factor in how a person will perform. For the pro athlete as well as many amateur athletes, knowledge regarding their glycogen stores, specifically the muscle glycogen stores of key muscles is highly desirable.
If the stores can be identified as being low, the person can proactively eat more carbohydrates. If the stores can be identified as being good, the person can avoid excessive eating—and therefore avoid having blood taken from the muscles to the stomach for digestion, as well as the potentially excess weight of the food or liquids providing the carbohydrates. More simply put it is important to eat enough but not too much, yet where that balance point is can shift throughout the day and from day to day.
Present methods for measuring glycogen involve the intrusive process of biopsy into the muscle tissue. Though generally a small incision, this insult into a finely tuned and trained muscle can cause soreness and or pain, and may well temporarily impede muscle operation as the muscle tissue works to repair itself. The resulting pain, soreness and repair process may degrade performance during the event or training.
The analysis of a biopsy to determine glycogen store is also a time consuming process and by the time the results are known, the metabolism of the body and specifically the muscle may well have changed the level of muscle glycogen store up or down such that the biopsy determination can only be valued as a general gauge of the glycogen levels at a past time.
Moreover, the value of determining the glycogen store within a muscle may be entirely offset by the minor injury to the muscle entailed by the biopsy process if the injury results in degraded muscle performance. Adding to that possibility the latency in biopsy determination and the value of intrusive biopsy process is even further diminished.
As such, although such knowledge could be quite advantageous in helping to insure peak performance for an event or training, present evaluation of glycogen stores are generally educated guesswork based on past biopsy testing. Though helpful, guesswork is clearly not ideal especially for pro athletes and the sponsors of pro athletes who may invest significant sums of money, training time and sacrifice in the effort to be prepared for a specific event.
Knowledge of muscle glycogen stores is not strictly limited to athletes. Indeed, many people in many different settings could well be aided by knowing their own glycogen stores or the glycogen stores of those they work with and/or care for. For example the determination of glycogen stores in the muscles of a hospital patient could improve adjustments to his or care and nutrition. Likewise such knowledge could beneficially aid in the care of the elderly or infirm, and persons with certain medical conditions such as, but not limited to, diabetes might benefit from knowing glycogen muscle stores.
Hence there is a need for a method and system that is capable of providing non-invasive determination of glycogen stores, and to do so in near real time.